1. Field of the Invention
The invention generally relates to a bioerodible implantable medical devices. Particularly, the invention relates to a drug eluting bioerodible implantable medical device, including a stent.
2. Description of Related Art
Percutaneous transluminal coronary angioplasty (PTCA) is a procedure for treating heart disease. This procedure generally entails introducing a catheter assembly into the cardiovascular system of a patient via the brachial or femoral artery, and advancing the catheter assembly through the coronary vasculature until a balloon portion thereon is positioned across an occlusive lesion. Once in position across the lesion, the balloon is inflated to a predetermined size to radially compress against the atherosclerotic plaque of the lesion to remodel the vessel wall. Subsequently, the balloon is deflated to allow the catheter assembly to be withdrawn from the vasculature.
While PCTA is widely used, it suffers from two unique problems. First, the blood vessel may suffer acute occlusion immediately after or within the initial hours after the dilation procedure. Second, the re-narrowing of an artery or other blood vessel after an initially successful angioplasty sometimes results. This blood vessel re-narrowing is commonly referred to as “restenosis,” which typically occurs within the first six months after angioplasty. Restenosis is believed to be due to, among other things, the proliferation and migration of cellular components from the arterial wall, as well as through geometric changes in the arterial wall referred to as “remodeling.”
To reduce occlusion of the artery or blood vessel, and the development of thrombosis and/or restenosis, an expandable stent is implanted in the lumen to maintain the vascular patency. Typically, expandable stents are formed from metal, including for example, 316 stainless steel, MP35N alloy and superelastic nickel-titanium. Additionally, it has become common to coat the implantable metal stent with particular drugs to prevent restenosis. One drawback of metal stent implants is stent occlusion, which may occur due to collapse of the stent. To overcome such disadvantages, bioerodible or bioabsorbable stents have been proposed, for example, in U.S. Pat. No. 6,287,332 to Bolz and U.S. Patent Publication No. 2004/0138738 to Stinson, the entire contents of each of which are incorporated herein by reference. However, there remains a need for an improved bioerodible medical device, including bioerodible stents.